SUMMARY OF WORK Software development on the full 3D model is proceding. The 2D grid model has been revised to include detailed balancing of whole-cell calcium balance. This model has been entirely recoded in compiled Java and spun out to run concurrently on all 48 processors of our local cluster with >70% efficiency. This has made it possible to explore parameters and identify several different new regimes of propagation relevant to the pacemaking function of SR calcium release in sin0-atrial node cells. The model is now running to accumulate event statistics, which is nearly completed and a publication on this model is in preparation.